Staphylococcus aureus is a significant cause of morbidity and mortality in the United States. This pathogen is a major concern because of the increasing number of antibiotic resistant strains isolated from both hospital and community settings. Infection by S. aureus can cause a severe inflammatory response in all major organs. Like most pathogens, S. aureus requires iron for growth and the preferred iron source during infection is heme. Following heme acquisition, staphylococcal heme degrading enzymes catalyze the release of free iron. Heme can also be preferentially segregated to the membrane intact, presumably for use as a membrane cofactor. This suggests that S. aureus differentially utilizes heme depending on its metabolic needs. Paradoxically, many pathogens that acquire heme can also synthesize heme de novo. It is currently unknown how heme acquisition and heme synthesis are coordinated within the cell. Based on our preliminary data we hypothesize that heme is differentially sorted depending on whether it is exogenously acquired versus endogenously synthesized. This application proposes to test this hypothesis by identifying the molecular recipients of heme in the plasma membrane. These studies will significantly increase our understanding of staphylococcal heme trafficking and respiration, and may lead to the identification of novel therapeutic targets. The specific aims of this application are: Aim 1. Determine the intracellular fate of exogenously acquired heme within staphylococci. Aim 2. Define the physiological contributions of endogenous heme during staphylococcal infection. PUBLIC HEALTH RELEVANCE: Staphylococcus aureus is a major cause of morbidity and mortality in the United States. The goal of this application is to determine how S. aureus modifies heme trafficking in response to environmental cues. These experiments will identify novel heme-binding proteins that may represent therapeutic targets.